I am not so familiar with cham eggs, but I have had success with wd eggs. Temps sound low to me - maybe they should be around 83 degrees or so? I place mine on MOIST perlite, buried 3/4 deep, with moss over the top so when I mist, the eggs don't get wet. When the perlite begins to dry out, I add a little distilled water down the sides of the tub, again so the eggs don't get wet.